ASSESSMENT OF THE EFFECT OF A COMPLEX OF ANTIGENS FROM OPPORTUNISTIC BACTERIA ON THE ACTIVATION OF CD54 RECEPTOR EXPRESSION BY HUMAN PROMONOCYTIC CELL LINE U937

Abstract

Opportunistic pathogens play a significant role in the development of respiratory infections, characterized by high morbidity and mortality. A promising approach involves the use of drugs based on antigens of opportunistic bacteria that stimulate the immune system. An important task in their development is the identification of evaluation methods and markers reflecting the enhancement of the immune response. Stimulation of myeloid cells is known to be of particular interest for this purpose. The U937 human promonocytic cell line is widely used as a model to analyze the functional activity of monocytes and macrophages. The expression of the CD54 (ICAM-1) receptor significantly increases on the surface of immune cells under inflammatory stimulation, making it a suitable marker for assessing innate immune activation, including in U937 cells. This study examined CD54 expression in U937 cells in response to two variants of the antigen complex of opportunistic bacteria: with and without the addition of an immunostimulatory copolymer. The antigen complex included antigens from four species: Escherichia coli, Proteus vulgaris, Staphylococcus aureus, Klebsiella pneumoniae. The additional immunostimulating agent was a copolymer of 2-methyl-5-vinylpyridine and N-vinylpyrrolidone hydrochloride. CD54 expression on U937 cells was assessed using flow cytometry. Cells were stimulated with S. aureus peptidoglycan (positive control) and the two antigen complex variants. Activation was evaluated using an activation coefficient, reflecting the increase in CD54 expression. A coefficient of ≥50% for the positive control indicated a robust response, while ≥30% was considered significant for the test samples. Both antigen complex variants and the positive control induced dose-dependent increases in CD54 expression, with an optimal concentration of 25 µg/mL. The observed effect confirmed the ability of the antigen complex of opportunistic pathogens to activate monocyte-macrophage cells and enhance the innate immune response. The obtained results emphasize the importance of using ICAM-1 as a marker of immune cell activation. The tested method proves to be promising for evaluating the effectiveness of drugs based on opportunistic bacteria.